U.S. patent application number 14/005000 was filed with the patent office on 2014-01-02 for photonic spectrometry device and method, method for calibrating the device, and use of the device.
This patent application is currently assigned to AREVA NP. The applicant listed for this patent is Eric Berruyer. Invention is credited to Eric Berruyer.
Application Number | 20140003579 14/005000 |
Document ID | / |
Family ID | 45841475 |
Filed Date | 2014-01-02 |
United States Patent
Application |
20140003579 |
Kind Code |
A1 |
Berruyer; Eric |
January 2, 2014 |
PHOTONIC SPECTROMETRY DEVICE AND METHOD, METHOD FOR CALIBRATING THE
DEVICE, AND USE OF THE DEVICE
Abstract
A photonic spectrometry device is provided. The photonic
spectrometry device comprises several identical spectrometers each
spectrometer comprising a radiation sensor and being capable of
providing a measurement spectrum corresponding to the measurements
of the sensor during a time interval, the spectrometers being
capable of performing measurements simultaneously on one same
radiation-emitting product and of providing measurement spectra for
one same time interval, and a processor capable of determining a
net spectrum from each of the measurement spectra provided by the
spectrometers for one same time interval, and of determining a
global spectrum resulting from the summation of the net spectra
determined for one same time interval.
Inventors: |
Berruyer; Eric; (Loriol Sur
Drome, FR) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Berruyer; Eric |
Loriol Sur Drome |
|
FR |
|
|
Assignee: |
AREVA NP
Courbevoie
FR
|
Family ID: |
45841475 |
Appl. No.: |
14/005000 |
Filed: |
March 12, 2012 |
PCT Filed: |
March 12, 2012 |
PCT NO: |
PCT/EP2012/054256 |
371 Date: |
September 13, 2013 |
Current U.S.
Class: |
378/82 |
Current CPC
Class: |
G01T 1/36 20130101; G01T
1/362 20130101; G01T 1/40 20130101 |
Class at
Publication: |
378/82 |
International
Class: |
G01T 1/36 20060101
G01T001/36 |
Foreign Application Data
Date |
Code |
Application Number |
Mar 14, 2011 |
FR |
1152069 |
Claims
1 to 15. (canceled)
16. A photonic spectrometry device comprising: several identical
photon spectrometers, each spectrometer comprising a radiation
sensor and being capable of providing a measurement spectrum
corresponding to the measurements of the sensor during a time
interval, the spectrometers being capable of performing
measurements simultaneously on one same radiation-emitting product
and of providing measurement spectra for one same time interval;
and a processor capable of determining a net spectrum from each of
the measurement spectra provided by the spectrometers in one same
time interval, by aligning the measurement spectrum provided by
each spectrometer in relation to a spectral line of a measurement
spectrum of the spectrometer corresponding to at least one
calibration source, and in relation to a reference line of the or
of each calibration source, and of determining a global spectrum
resulting from the summation of the net spectra determined for one
same time interval.
17. The photonic spectrometry device as recited in claim 16 wherein
each spectrometer comprises a detection module capable of
converting an electric signal emitted by the sensor on detection of
a photon and proportional to the energy of the detected photon, to
a digital signal representing the energy of the detected
photon.
18. The photonic spectrometry device as recited in claim 17 wherein
each detection module is adjustable so as to adjust the digital
signal provided by the detection module detection as a function of
the signal emitted by the associated sensor.
19. The photonic spectrometry device as recited in claim 18 wherein
each spectrometer is initially adjusted by calibrating the
detection module such that the sensor/detection module pairs of the
spectrometers emit substantially the same digital signal in the
presence of one same radiation source.
20. The photonic spectrometry device as recited in claim 16 further
comprising at least one radiation-emitting calibration source
common to the spectrometers, each sensor of the spectrometers
statistically receiving substantially one same quantity of photons
derived from the or from each calibration source in one same time
interval.
21. The photonic spectrometry device as recited in claim 20 wherein
the at least one radiation-emitting calibration source common
comprises at least two different calibration sources common to the
spectrometers.
22. The photonic spectrometry device as recited in claim 21 wherein
the at least two different calibration sources include two
calibration sources having respective reference spectral lines
located either side of a characteristic spectral line of an element
to be detected.
23. The photonic spectrometry device as recited in claim 21 wherein
the element to be detected is uranium 235.
24. The photonic spectrometry device as recited in claim 16 wherein
the processor is capable of determining each net spectrum by
aligning each measurement spectrum in relation to a characteristic
spectral line of the measurement spectrum corresponding to the or
to each calibration source and in relation to a reference line of
the or of each calibration source.
25. The photonic spectrometry device as recited in claim 16 wherein
the processor is capable of determining at least one alignment
function to align the measurement spectra of a spectrometer using a
reference measurement spectrum of the spectrometer, the or each
alignment function being determined so as to cause the coinciding,
for each calibration source, of a characteristic spectral line of
the reference measurement spectrum with the reference spectral line
of the corresponding calibration source.
26. The photonic spectrometry device as recited in claim 16 wherein
the photonic spectrometry device measures gamma-rays or X-rays.
27. A method for calibrating the photonic spectrometry device as
recited in claim 16, comprising the step of: adjusting a detection
module capable of converting an electric signal output from the
sensor of each spectrometer to a digital signal representing the
energy of each detected photon so that the spectrometers provide
substantially identical spectra in the presence of one same
radiation source.
28. A method of operating the photonic spectrometry device as
recited in claim 16, comprising: measuring, by the photonic
spectrometry device, uranium 235 content of hydrofluoric acid
resulting from the production of uranium oxide; measuring, by the
photonic spectrometry device, the content of at least one
radio-isotope in effluent from a plant recycling radioactive
materials; or measuring, by the photonic spectrometry device,
before discharge, the content of at least one radio-isotope in
effluent from a plant treating radioactive materials.
29. A photonic spectrometry method comprising the steps of:
providing measurement spectra using identical spectrometers, each
measurement spectrum resulting from measurements performed on one
same radiation-emitting product during one same time interval by a
respective one of the spectrometers; determining a net spectrum
from each measurement spectrum by aligning the measurement spectrum
in relation to at least one spectral line of a measurement spectrum
provided by the spectrometer, the or each spectral line
corresponding to a calibration source and in relation to the
reference line of the or of each calibration source; and
determining a global spectrum resulting from the summation of the
net spectra.
30. The method as recited in claim 29 wherein each net spectrum is
determined from each measurement spectrum provided by a
spectrometer by aligning the measurement spectrum in relation to a
spectral line of the measurement spectrum provided by the
spectrometer, the spectral line corresponding to at least one
calibration source, and in relation to a reference line of the or
of each calibration source.
31. The method as recited in claim 29 wherein at least one
alignment function is determined for the alignment of the
measurement spectra of a spectrometer from a reference measurement
spectrum provided by the spectrometer, the or each alignment
function being determined so as to cause the coinciding, for the or
each calibration source, of a characteristic spectral line of the
reference measurement spectrum with the reference spectral line of
this calibration source.
Description
[0001] The present invention relates to the field of photon
spectrometry.
BACKGROUND
[0002] The production or recycling of nuclear fuel leads to the
production of by-products, waste or effluent. It must be verified
that the content of radioactive materials in these by-products,
waste and effluent is acceptable with regard to regulatory
thresholds.
[0003] For example, uranium oxide (UxOy) and in particular uranium
dioxide (UO2) is used as nuclear fuel. Uranium oxide is obtained
for example by conversion of uranium hexafluoride (UF.sub.6) to
uranium oxide. Conversion is conducted in a furnace for example by
counter-current circulation of a powder of uranium hexafluoride and
water (H.sub.2O). Said manufacturing process is described in FR 2
771 725.
[0004] This conversion generates hydrofluoric acid (HF) as
recyclable by-product. It must be controlled that the concentration
of uranium in the hydrofluoric acid does not exceed the regulatory
thresholds laid down by the nuclear safety agency.
[0005] To do so, it is possible regularly to take samples and to
have them analysed by a laboratory, for example using mass
spectrometers, molecular absorption spectrophotometers . . .
[0006] Nevertheless, such analyses require the use by qualified
personnel of sophisticated laboratory equipment that is costly to
purchase, maintain and operate. They require a time possibly
varying from several tens of minutes to a day depending on the
necessary preparations and the type of measurement to be performed.
They are conducted at regular time intervals but spaced apart.
These analyses are ill-adapted to the monitoring of a continuous
industrial process and in this case necessitate intermediate
storage and treatment in batches at certain steps of the industrial
process.
SUMMARY OF THE INVENTION
[0007] It is one objective of the invention to propose a photonic
spectrometry device adapted for the monitoring of industrial
processes.
[0008] For this purpose a photonic spectrometry device is provided
comprising several identical photonic spectrometers, each
spectrometer comprising a radiation sensor and being capable of
providing a measurement spectrum corresponding to the measurements
of the sensor during a time interval, the spectrometers being
capable of performing measurements simultaneously on one same
radiation-emitting product and of providing measurement spectra for
one same time interval, and processing means capable of determining
a net spectrum from each of the measurement spectra provided by the
spectrometers during one same time interval and of determining a
global spectrum resulting from the summation of the net spectra
determined for one same time interval.
[0009] According to other embodiments, the photonic spectrometry
device comprises one or more of the following characteristics taken
alone or in any possible technical combination: [0010] each
spectrometer comprises a detection module capable of converting an
electric signal emitted by the sensor on detection of a photon and
proportional to the energy of the detected photon, to a digital
signal representing the energy of the detected photon; [0011] each
detection module is adjustable so as to adjust the digital signal
output by the detection module as a function of the signal emitted
by the associated sensor; [0012] each spectrometer is initially
adjusted by calibrating the detection module so that the
sensor/detection module pairs of the spectrometers emit
substantially the same digital signal in the presence of one same
source of radiation; [0013] at least one calibration source
emitting radiation, common to the spectrometers, each sensor of the
spectrometers statistically receiving substantially one same
quantity of photons from the or from each calibration source for
one same time interval; [0014] the sensors of the spectrometers are
arranged in a circle; [0015] the sensors are regularly distributed
around the circle; [0016] at least two different calibration
sources common to the spectrometers; [0017] two calibration sources
having respective reference spectral lines located either side of a
characteristic spectral line of an element to be detected, in
particular either side of a spectral line characteristic of uranium
235; [0018] the processing means are capable of determining each
net spectrum by aligning each measurement spectrum in relation to a
spectral line of the measurement spectrum corresponding to the or
to each calibration source, and in relation to a reference line of
the or of each calibration source; [0019] the photonic spectrometer
device is adapted for the measurement of gamma-rays or the
measurement of X-rays.
[0020] A photonic spectrometry method is also provided comprising
the steps of: [0021] providing measurement spectra using identical
spectrometers, each measurement spectrum resulting from
measurements performed on one same radiation-emitting product
during one same time interval by a respective spectrometer; [0022]
determining a net spectrum from each measurement spectrum; [0023]
determining a global spectrum resulting from the summation of the
net spectra.
[0024] According to one embodiment, each net spectrum is determined
by aligning the measurement spectrum provided by a spectrometer in
relation to a spectral line of the measurement spectrum
corresponding to at least one calibration source and in relation to
the reference line of the or of each standard source.
[0025] A method for calibrating a photonic spectrometry device is
also provided comprising the step to adjust a detection module
capable of converting an electric signal output by the sensor of
each spectrometer to a digital signal representing the energy of
each detected photon so that the spectrometers provide
substantially identical spectra in the presence of one same source
of radiation.
[0026] A use of a photonic spectrometry device is also provided
such as defined above to measure the uranium content of
hydrofluoric acid resulting from the production of uranium oxide,
to measure the content of at least one radio-isotope in effluent
from a plant recycling radioactive materials, or to measure before
discharge the content of at least one radio-isotope in the effluent
of a plant for the treatment of radioactive material.
BRIEF SUMMARY OF THE DRAWINGS
[0027] The invention and its advantages will be better understood
on reading the following description given solely as an example and
with reference to the appended drawings in which:
[0028] FIG. 1 is a schematic view illustrating a photonic
spectrometry device according to an embodiment of the
invention;
[0029] FIG. 2 is a schematic view of a photon spectrometer of the
photonic spectrometry device shown in FIG. 1;
[0030] FIGS. 3 and 4 are cross-sectional and overhead views of a
detection assembly of the device in FIG. 1;
[0031] FIG. 5 is a diagram illustrating a spectrum obtained using a
spectrometer of the photonic spectrometry device in FIG. 1;
[0032] FIGS. 6 to 8 are schematic views of plants for producing or
recycling nuclear fuel incorporating a photonic spectrometry device
according to embodiments of the invention.
DETAILED DESCRIPTION
[0033] The photonic spectrometry device 2 illustrated in FIG. 1 is
capable of measuring radiation emitted by a product 4.
[0034] The photonic spectrometry device 2 comprises several photon
spectrometers 6 and an electronic processing module 8, hereinafter
<<processing module>>. The photonic spectrometry device
2 comprises a data exchange bus 10 connecting the processing module
8 to the output of each spectrometer 6.
[0035] Each spectrometer 6 is capable of producing a spectrum of
the number of photons detected during a time interval or
measurement interval as a function of the energy of the detected
photons. Each spectrometer 6 is designed to ensure the linearity of
its response (energy spectrum) in relation to its input data
(energy of each photon).
[0036] Each spectrometer 6 comprises a single radiation sensor 12
and an associated electronic detection and quantification module
14, hereinafter <<detection module>>, and associated
electronic analysis module 16 hereinafter <<analysis
module>>.
[0037] The sensor 12 is capable of detecting gamma photons also
called gamma-rays and/or X photons also called X-rays and, for each
detected photon, of emitting an electric output signal proportional
to the energy of the detected photon. The sensor 12 is electrically
powered by a high voltage electric energy source 18.
[0038] The detection module 14 on its input receives the output
signal of the associated sensor 12 and outputs a digital signal
representing the value of the energy of each photon detected by the
sensor 12. The detection module 14 is electrically powered by a low
voltage electric energy source 20.
[0039] The analysis module 16 is capable of counting the signals
emitted by the detection module 14, each signal corresponding to a
photon detected by the sensor 12, and of producing a measurement
spectrum of the quantity of photons detected by the sensor 12 as a
function of energy (keV) over a measurement interval.
[0040] The sensor 12, the detection module 14 and the analysis
module 16 are separate and connected together by data transmission
links. The sensor 12 outputs an electric signal. The input of the
detection module 14 is connected to the output of the sensor 12 via
a wire link 22. The detection module 14 emits an optical digital
output signal. The input of the analysis module 16 is connected to
the output of the detection module 14 via an optical link 24
typically an optical fibre.
[0041] The spectrometers 6 are capable of operating simultaneously
and of simultaneously processing the photons emitted by the product
4.
[0042] The processing module 8 is connected to the output of each
spectrometer 6 by the bus 10. The processing module 8 is configured
to perform specific processing of the measurement spectra acquired
simultaneously during the same time interval and produced by the
spectrometers 6 so that it is possible to deliver a representative
global spectrum determined from all the measurement spectra.
[0043] The processing module 8 is connected to a man/machine
interface 26 to display results and/or receive instructions.
[0044] The processing module 8 is connected to a driver unit 28
capable of using the result given by the processing module 8 to
drive a plant 30, e.g. a plant for producing or recycling nuclear
fuel or an installation to evacuate effluent from a plant producing
and/or recycling nuclear fuel.
[0045] The spectrometers 6 are identical. The sensors 12 of the
spectrometers 6 are identical, the detection modules 14 of the
spectrometers 6 are identical and the analysis modules 16 of the
spectrometers 6 are identical.
[0046] As shown in FIG. 2 illustrating a spectrometer 6, the sensor
12 of each spectrometer 6 is a scintillation sensor. It comprises a
scintillator crystal 32 e.g. an inorganic scintillator of doped
alkali halide type such as NaI(T1) for example or of mineral
compound type such as LaBr.sub.3(Ce), and a photomultiplier 34
optically coupled to the crystal 32. When a photon is absorbed by
the crystal 32, the latter emits a light signal whose energy is
proportional to the energy of the absorbed photon. The
photomultiplier 34 outputs an electric signal proportional to the
light energy emitted by the crystal 32.
[0047] The sensor 12 therefore outputs an analogue electric signal
proportional to the energy released by the photon in the crystal
32.
[0048] The detection module 14 comprises an analogue/digital
converter 36 to convert the analogue input signal to a digital
output signal.
[0049] The detection module 14 is adjustable so as to adjust the
signal output by the detection module 14 in relation to the input
signal it receives. To do so the detection module 14 comprises a
proportional controller 38 capable of applying a multiplication
coefficient to the signal it receives. The proportional controller
38 is adjustable so that it is possible to adjust the
multiplication coefficient.
[0050] Returning to FIG. 1, the photonic spectrometry device 2
comprises at least one calibration source and preferably at least
two calibration sources S1, S2 associated with the plurality of
spectrometers 6. Each calibration source S1, S2 emits a determined
spectrum of photons. The calibration sources S1, S2 emit different
photon spectra. Preferably, each calibration source S1, S2 emits a
spectrum having a characteristic spectral line around a reference
energy or reference line and the calibration sources S1, S2 have
one or more reference lines at different reference energies.
[0051] The calibration sources S1, S2 are arranged so as to ensure
identical irradiation of each sensor 12 of each spectrometer 6. For
example, to ensure identical irradiation, each calibration source
S1, S2 is arranged equidistant from the sensors 12 of the
spectrometers 6. In other words, the spectrometers 6 use at least
one common calibration source S1, S2, preferably two common
calibration sources S1, S2.
[0052] The calibration sources S1, S2 are separate from the
spectrometers 6 and in particular from the sensor 12 of each
spectrometer 6. Each spectrometer 6 is therefore associated with at
least one calibration source S1, S2 separate from the sensor 12 of
this spectrometer 6, preferably with two calibration sources S1, S2
separate from the sensor 12 of this spectrometer 6.
[0053] The processing module 8 is capable of individually analysing
each measurement spectrum during a given measurement interval so as
to compare, for each spectrometer 6, the measured characteristic
spectral line corresponding to each calibration source S1, S2 with
the corresponding reference line, of calculating the affine
function constants to be applied to cause the coinciding of the
measured characteristic spectral lines of the sources S1, S2 with
their reference lines, of applying the affine functions to every
point of the spectral domain to align the measurement spectrum and
thereby determine a corresponding net spectrum, and finally of
summing the net spectrum derived from each of the spectrometers 6
to obtain the global spectrum.
[0054] Alignment is energy-based and/or efficacy-based. Energy
alignment consists of determining an affine function to cause the
energy of the measured characteristic spectral line corresponding
to the or each calibration source S1 and S2 to coincide with the
energy of the reference line of the or of each calibration source
S1, S2. Efficacy-based alignment consists of determining an affine
function to cause the number of detected photons of the measured
characteristic spectral line corresponding to the or to each
calibration source S1 et S2 to coincide with the expected number of
photons--i.e. the initial detection efficacy of the sensor 12 of
the Spectrometer 6 concerned--during the measurement interval.
[0055] The processing module 8 receiving the measurement spectra
and/or the analysis module 16 producing the measurement spectra
is/are advantageously capable of storing these at least
temporarily. This makes it possible to consult the measurement
spectra for qualification purposes for example or for a control in
the event of an anomaly or operating incident.
[0056] Processing means are formed by the processing module 8
capable of determining a net spectrum from each of the measurement
spectra provided by the spectrometers 6 and of determining a global
spectrum resulting from summation of the net spectra.
[0057] In one variant, the analysis module 16 of each spectrometer
6 is capable of determining the measurement spectrum and of
performing the processing thereof to determine the corresponding
net spectrum. In this case, the processing means are formed by the
analysis module 16 of each spectrometer 6 and by the processing
module 8 which receives the net spectra determined by the analysis
modules 16 and performs summation thereof to obtain the global
spectrum.
[0058] As illustrated in FIGS. 3 and 4, the sensors 12 are
regularly distributed over an imaginary circle of sensors C1
centred on an axis of symmetry A. As illustrated in FIG. 4, the
sensors 12 total a number of 8 and are distributed around the axis
A, with the same metric radius value and at a regular angular pitch
of 45.degree..
[0059] The calibration sources S1, S2 are arranged at the centre of
the circle of sensor C1. Each calibration source S1, S2 therefore
lies equidistant from the sensors 12. As a result each sensor 12
statistically receives substantially the same quantity of photons
derived from the calibration sources S1, S2, during one same
measurement interval.
[0060] The photonic spectrometric device 2 comprises a chamber 40
for circulation of the product 4 to be controlled, having symmetry
of revolution about the axis of symmetry A. Therefore each sensor
12 statistically receives substantially the same quantity of
photons derived from the product 4 present in the chamber 40.
[0061] The sensors 12 are arranged on the chamber 40 so that space
receiving the product 4 in the chamber 40 lies between the sensors
12 and around the sensors 12. This ensures good irradiation of the
sensors 12 by the photons emitted by the product 4.
[0062] As illustrated in FIGS. 3 and 4, the chamber 40 comprises a
tank 42 of circular cross-section extending along the axis of
symmetry A, and a lid 44 of circular contour hermetically sealing
the tank 42 if necessary.
[0063] The lid 44 is of general circular shape. The lid 44
comprises at least one filling device 48 arranged close to the
centre of the lid 44 coinciding with the axis A and ensuring rapid
filling of the chamber 40 and at least one discharge device 46
positioned on the periphery of the lid 44 and ensuring evacuation
of the overflow of the pot 40. As illustrated in FIGS. 3 and 4 when
several filling devices 48 are present, the filling devices 48 are
spaced apart and regularly distributed in a circle centred on the
axis A. Depending on the configuration of the plant 30 the filling
device 48 may also be arranged on a side face or the inner face of
the tank 42.
[0064] The tank 42 comprises at least one drainage device 56 which
is fed at the lowest point of the tank 42 and ensures the draining
of the pot 40 controlled by an evacuation valve 58. As illustrated
in FIG. 3, the tank 42 comprises a drainage device 56 located at
the centre of the bottom of the tank.
[0065] The lid 44 comprises a plurality of sensor alveoli 50
projecting inside the chamber 40 and open towards the outside of
the chamber 40. Each sensor alveolus 50 defines a housing in the
lid 44 to receive a sensor 12. The sensor alveoli 50 are arranged
following the circle of sensors C1. The sensor alveoli 50 are
distributed at a regular angle about the axis A.
[0066] The lid 44 comprises a plurality of retaining devices 52 for
the detection modules 14 and opening towards the outside of the
chamber 40. Each retaining device 52 by projecting on the outside
of the lid 44 defines a housing to receive a detection module 14.
The retaining devices 52 are arranged in an imaginary circle of
detection modules C2 centred on the axis A. The retaining devices
52 are distributed at regular angle about the axis A.
[0067] The lid 44 comprises an alveolus 54 for calibration source
centred on the axis A. The calibration source alveolus 54 is
arranged between the filling devices 48. The calibration sources
S1, S2 are arranged in the calibration source alveolus 54. Each
calibration source S1, S2 lies in the centre of the circle of
sensors C1 around which the sensors 12 are arranged.
[0068] The chamber 40 is arranged in the vicinity of a plant 30.
The detection assembly formed by the measuring chamber 40, the
sensors 12 and their associated detection modules 14 is fed with
product 4 to be controlled via a direct line or branch line
(parallel line) of the plant 30.
[0069] The chamber 40 is arranged for example at the output of a
furnace producing uranium and hydrofluoric acid, on an output of
liquid hydrofluoric acid, in a confined room.
[0070] The detection modules 14 arranged in the vicinity of the
sensors 12 allow the use of short wire links 22 between the
detection modules 14 and the sensors 12, to maximize the
signal-to-noise ratio during detection.
[0071] The analysis modules 16 associated with the detection
modules 14 and with the sensors 12 can be placed outside the
confined room. The optical link 24 via optical fibre ensures the
transmission of data at a fast rate and reliably over long
distances for example over several tens of metres.
[0072] When in operation, during a determined time interval, the
spectrometers 6 simultaneously measure the photons emitted by the
product 4 present in the measuring chamber. Each spectrometer 6
provides a measurement spectrum. After individual alignment of each
measurement spectrum to determine a net spectrum, the processing
module 8 adds the net spectra to determine a global spectrum
resulting from summation of the net spectra. On the basis of the
global spectrum the processing module 8 determines one or more
measurements, for example a concentration of uranium 235 in the
product 4.
[0073] The photonic spectrometry device 2 allows a measurement
performed by laboratory equipment on a sample of product 4 over a
period of time T, to be replaced by n simultaneous measurements
(n>1) on the product 4 at the output of a plant 30 and performed
by several spectrometers 6 whilst guaranteeing a result of same
statistical accuracy acquired over a shorter time period possibly
being reduced to T/n.
[0074] The photonic spectrometry device 2 allows satisfactory
measurements to be performed over a measurement interval of a few
minutes e.g. 1 to 5 minutes, whereas conventional sampling and
analysis techniques using laboratory equipment require several tens
of minutes even several hours and also, depending on the product to
be sampled, action by a human operator in a possibly hazardous area
such as a confined area.
[0075] The photonic spectrometry device 2 therefore allows
measurements to be performed very rapidly over a measurement
interval compatible with the monitoring of an industrial process or
the driving of an industrial process.
[0076] Nonetheless, spectrometry is measurement of statistical
type. Not all the photons emitted by the product 4 during the
measurement interval are necessarily detected. Each sensor 12 only
detects part of the photons which reach the sensor 12.
[0077] The principle of the adding of measurements provided by
different spectrometers 6 can only be considered to be physically
justified if the photonic spectrometry device 2 verifies the
principle of ergodicity.
[0078] In practice this means that it must be possible for the
different measuring pathways of one same magnitude to be considered
as identical or substantially identical so as to provide identical
or sufficiently identical results under the same measuring
conditions.
[0079] To meet this condition or at least to be sufficiently close
to meeting this condition, the photonic spectrometry device 2
comprises several identical spectrometers 6.
[0080] In practice owing to unavoidable manufacturing tolerances,
although the sensors 12 are identical they have manufacturing
dispersion and when placed under the same conditions give different
measurements.
[0081] The value of the signals output by a sensor 12 also depends
on its high voltage supply. A modification however small in
relative value of this high voltage supply substantially modifies
the value of the signals produced. The adjustment of this voltage
individually for each sensor 12 could in theory allow calibration
of the sensors 12, but this individual adjustment requires a
specific high voltage electric energy source 18 per sensor 12 and
is not industrial on account of the high maintenance involved. To
meet the constraints of an industrial process it is preferable to
maintain a single high voltage value, which could allow the use a
single high voltage electric energy source 18 for all the sensors
12. All the sensors 12 being powered by the same high voltage
value, the output signals will then be different through the
differences in gain and detection yield of each sensor 12.
[0082] According to one aspect of the invention, the sensor 12 of
each spectrometer 6 is coupled to the detection module 14
associated with this spectrometer 6. The sensor 12 and the
associated detection module 14 are jointly calibrated.
[0083] According to one embodiment, the detection module 14 of each
spectrometer 6 is initially adjusted so that the signals given by
the different sensor 12/detection module 14 pairs are identical and
linear or substantially identical and linear under the same
measuring conditions.
[0084] Advantageously each sensor 12/detection module 14 pair is
adjusted by adjusting the gain of the photomultiplier 34 coupled to
the crystal 32 of the sensor 12, then by adjusting the detection
module 14 for example by adjusting the proportional controller 38
of the detection module 14.
[0085] Therefore, according to this embodiment of the invention,
adjustment is performed at each sensor 12/detection module 14 pair
and not at each sensor 12. This makes it possible to take into
account the dispersion between sensors 12 and between detection
modules 14 and to ensure that each spectrometer 6 produces
substantially the same net spectrum in the presence of one same
radiation source.
[0086] The initial adjustment of each spectrometer 6 is conducted
for example in the presence of at least one calibration source S1,
S2. The proportional controller 38 of the detection module 14 is
adjusted so that the output signals from the detection module 14
correspond to the expected values in the presence of the
calibration source S1, S2.
[0087] As a result each sensor 12 and the detection module 14
associated therewith form an inseparable pair. Two detection
modules 14 cannot be changed over without changing over the two
associated sensors 12, and a sensor 12 cannot be replaced without
associating its own detection module 14 together with it.
[0088] The sensors 12 are powered by the same high voltage value
and are advantageously powered by the same high voltage electric
energy source 18. This simplified powering of the sensors 12 and
maintenance operations. For other reasons such as the principle or
redundancy used in nuclear plants as illustrated in FIG. 1, it is
possible to provide a high voltage electric energy source 18 that
is common to two sensors 12 for example. In FIG. 1 the
spectrometers 6 are grouped in pairs, the two sensors 12 of the
spectrometers 6 of each group being powered by the same high
voltage electric energy source 18.
[0089] Each sensor 12 may drift over time and the sensors 12 may
have different drifts.
[0090] According to one aspect of the invention, the photonic
spectrometry device 2 comprises at least one calibration source S1,
S2 common to the different spectrometers 6 to correct the drift of
the sensors 12. The sensors 12 are arranged symmetrically around
each calibration source S1, S2. Therefore the correction of the
drift of the sensors 12 is conducted from the same calibration
source S1, S2 thereby providing an additional guarantee for heed of
the principle of ergodicity.
[0091] The drift of each sensor 12 is corrected by alignment of
each measurement spectrum in relation to the measured
characteristic spectral line corresponding to the or to each
calibration source S1, S2 and in relation to the reference line of
the or of each calibration source S1, S2 so as to determine a net
spectrum of radiation emitted by the product 4 and by the or each
calibration source S1, S2.
[0092] According to one aspect of the invention, the photonic
spectrometry device 2 comprises at least one calibration source S1
having a reference energy higher than that of an element to be
detected.
[0093] Uranium isotope 235 inter alia has a characteristic gamma
photon emission at a value of 185.7 keV. A photonic spectrometry
device 2 adapted to the detection of uranium isotope 235 may
comprise a caesium 137 calibration source for example, having a
reference characteristic gamma photon emission at a value of 662
keV whose influence on counts at the energy of 185.7 keV, i.e.
counting results over the measurement interval output by the
analysis module 16, is easily made negligible.
[0094] By ensuring that each spectrometric pathway has a
characteristic of response linearity, it is possible to correct the
measurement spectrum as a function of the difference between the
measured value for a calibration source and the reference value of
the calibration source. An error--in relative value--of X % in the
measurement of the reference value of the calibration source leads
to a correction--in relative value--of X % of all measured
values.
[0095] As a result a small drift in measurement in absolute value
of the reference energy of a calibration source leads to a greater
correction in absolute value of all energy measurements higher than
that of the calibration source and a smaller correction in absolute
value of all energy measurements lower than that of the calibration
source. This means that for a given measurement uncertainty,
uncertainty is higher for all energy measurements higher than that
of the calibration source and lower for all energy measurements
lower than that of the calibration source.
[0096] The choice of an energy calibration source higher than the
energy of an element to be detected therefore allows the minimising
of measurement uncertainties in absolute value over the energy
ranges corresponding to that of the element to be detected.
[0097] According to one aspect of the invention the photonic
spectrometry device 2 comprises two calibration sources S1 and S2
having characteristic spectral lines with different reference
energies.
[0098] Preferably the reference energies of the calibration sources
S1 and S2 are chosen so as to have an emission energy which lies at
one of the two ends of the spectral energy analysis band of one
spectrometer 6 for one thereof, and for the other at the other end
of the spectral energy analysis band of the same spectrometer 6.
Therefore with two sources providing two different energies and the
most distant apart possible over the spectral analysis range,
correction is optimal for all the detectable photons on this energy
analysis band.
[0099] Uranium isotope 235 inter alia has a characteristic gamma
photon emission at a value of 185.7 keV. A photonic spectrometry
device 2 adapted for the detection of uranium 235 comprises a
calibration source in americium 241 for example having a reference
energy of 59.5 keV and hence a spectral reference energy line
around abscissa 60 keV and a calibration source in caesium 137
having a reference energy of 662 keV and hence a spectral reference
energy line around abscissa 662 keV.
[0100] FIG. 5 illustrates one example of a spectrum able to be
obtained in the presence of an americium 241 calibration source, a
caesium 137 calibration source and a sample containing uranium 235.
The abscissa represents the energy in keV of the received photons
and the ordinate the number of detected photons.
[0101] The correction of drift is made by correcting each
measurement spectrum as a function of the measured characteristic
spectral line and of the reference line of each calibration source
S1, S2, which guarantees more precise correction.
[0102] The affine functions for alignment are determined so that
the measured characteristic lines of the calibration sources S1, S2
used coincide, in energy and count, with the respective reference
lines of the calibration sources S1, S2 and are then applied to
each point of the measurement spectrum.
[0103] Most photon sensors comprise a calibration source--e.g.
americium 241--placed in the sealed sensor and even sealed to the
crystal at the time of manufacture. Subjected to regulations on
sealed sources, the calibration sources have a limited regulatory
lifetime. The source and hence the sensor must be destroyed at the
end of the regulatory lifetime irrespective of the state of the
sensor, which limits the lifetime of the sensor. Similarly if a
sensor is faulty, the whole sensor is replaced and the calibration
source is destroyed with the sensor.
[0104] The use of a calibration source associated with a sensor but
physically separate from the sensor therefore allows the limiting
of operating costs of the assembly by limiting the cost of
replacement of a sensor and allowing the sensor to be preserved
even if the calibration source must be replaced and vice versa.
Additionally, this allows the use of one same calibration source
for several sensors, which not only allows limiting of the cost of
the measuring assembly but also ensures better suitability with the
constraint of ergodicity of a device using several sensors
simultaneously.
[0105] In one embodiment, at least one alignment function to align
the measurement spectra of a spectrometer 6 is determined for each
measurement spectrum determined by the spectrometer 6. As a
variant, at least one alignment function to align the measurement
spectra of a spectrometer 6 is determined from at least one
reference measurement spectrum of the spectrometer 6 so as to cause
the coinciding, for each calibration source S1, S2, of a
characteristic spectral line of the reference measurement spectrum
with the reference spectral line of this calibration source S1, S2.
The, or each, alignment function is used to align several
successive measurement spectra of the spectrometer 6. The, or each,
alignment function is periodically determined at a periodicity
dependent on the stability of the spectrometer 6. The periodicity
may be in the order of one day, one week or more.
[0106] FIGS. 6 to 8 schematically illustrate industrial plants 30
using a photonic spectrometry device 2 to control the radio-isotope
content of by-products and discharged effluent.
[0107] FIG. 6 illustrates a plant for the conversion of uranium
hexafluoride to uranium oxide comprising a furnace 60 receiving
inter alia an input of uranium hexafluoride UF.sub.6 and water
H.sub.2O circulating in counter-current in the furnace 60, and
outputting uranium oxide U.sub.xO.sub.y as product and hydrofluoric
acid HF as by-product.
[0108] As illustrated the chamber 40 of the photonic spectrometry
device 2 is arranged in series on the hydrofluoric acid output
after condensation to liquid HF to verify that the uranium 235
content of the hydrofluoric acid is lower than regulatory
thresholds.
[0109] FIG. 7 illustrates a recycling plant of radioactive
materials comprising a reactor 62 into which waste is input
containing radioactive material WMF and reagents R able to
precipitate the radioactive material, and which outputs recycled
radioactive material RMF and effluent E.
[0110] As illustrated the chamber 40 of the photonic spectrometry
device 2 is arranged as a branch line (in parallel) on an effluent
output E to verify that the radio-isotope content of the effluent E
e.g. some radio-isotopes of thorium, uranium 235, lead 212, . . . ,
or other radioactive impurities derived for example from the use of
uranium derived from the processing of irradiated fuel called
reprocessed uranium, plutonium . . . is lower than regulatory
thresholds.
[0111] The recycling plant comprises a recirculation pipe 64
extending between the output of the measuring chamber 40 of the
photonic spectrometry device 2 and the waste input WMF so that the
effluent E is recycled for as long as its content of one or more
radio-isotopes is too high.
[0112] FIG. 8 illustrates an assembly 66 for treating radioactive
materials 66 comprising several treatment plants 68 of radioactive
materials producing effluent E collected in an evacuation circuit
for discharge thereof.
[0113] The photonic spectrometry device 2 is arranged in the
discharge circuit to verify that the radio-isotope content of the
collected effluent E conforms to regulatory discharge
thresholds.
[0114] The photonic spectrometry device 2 is installed in a main
pipe 70 to perform measurements on all the effluent E or on a
branch pipe to perform measurements on a fraction of the collected
effluent E.
[0115] It is possible to use the photonic spectrometry device 2 so
as to determine the origin of effluent pollution with radioactive
material. In relation to the industrial process from which
pollution e.g. uranium originates, chemical elements characteristic
of the process used may be associated with uranium. For example the
presence of lead 212 in association with uranium 235 is the sign of
pollution derived from a plant using reprocessed uranium.
[0116] Therefore according to one aspect of the invention, the
processing module 8 of the photonic spectrometry device 2 is
configured to determine, from the global spectrum, the presence of
additional radio-isotopes e.g. uranium 235.
[0117] In general the choice of the use of the photonic
spectrometry device 2 in series or in parallel on the output of the
product 4 to be controlled is dependent on the plant 30 and on the
flow rate of the product on the output line.
[0118] According to one option, the processing module 8 comprises a
memory in which reference spectra are stored characteristic of some
types of pollution, and is configured for example to emit an alert
or trigger stoppage of the plant 30 in the event that a net
spectrum corresponds to a pre-recorded reference spectrum.
[0119] With the invention it is possible to perform rapid
measurements of gamma -and/or X-rays compatible with the monitoring
or driving of industrial processes. The photonic spectrometry
device can be built from commercially available parts and can be
positioned in situ in the vicinity of or within a plant to control
the products output by this plant and/or to drive the plant.
[0120] The invention may particularly apply to the measurement of
uranium 235 content at the output of processes for the manufacture
of uranium-based nuclear fuel, or of uranium recycling processes.
In general, the invention applies to the measurement of the content
of any radioactive element.
[0121] The invention can be applied to any gamma-ray or X-ray
measurement. The spectrometers of the invention are gamma- and/or
X-ray photon spectrometers depending on the scintillator used.
* * * * *